A transmission mechanism included in a conventional vehicle drive device is capable of changing the speed range between a low range (L) and a high range (H) in response to, for example, a driver's operation of a range changing switch etc. (see, for example, Patent Literatures 1 and 2).
The transmission mechanism changes the ranges by, for example, sliding a clutch sleeve in the direction of an output shaft thereof and thereby connecting the clutch sleeve to a low gear or a high gear. The clutch sleeve is mounted externally around the output shaft of the transmission mechanism in a manner that allows the clutch sleeve to rotate together with the output shaft and moved in the axial direction.
The low and high gears each have, on the outer circumference thereof, a plurality of teeth (splines) that are circumferentially arranged and equally spaced. The clutch sleeve has, on the inner circumference thereof, a plurality of teeth (splines) that can be engaged with the teeth (splines) of the gears. When the inner teeth (splines) of the clutch sleeve are engaged (fitted) with the outer teeth (splines) of the low- or high gear, the clutch sleeve is connected to the low- or high gear.
When the clutch sleeve is slid in one direction along the shaft to be connected to the low gear, a power transfer path is established through which low-speed rotational power is transmitted from the low gear and the clutch sleeve to the output shaft, resulting in the “low range.”
When the clutch sleeve is slid in the opposite direction along the shaft to be connected to the high gear, a power transfer path is established through which high-speed rotational power is transmitted from the high gear and the clutch sleeve to the output shaft, resulting in the “high range.” Note that when the clutch sleeve is in neutral position in which the clutch sleeve is connected neither to the low gear nor to the high gear, a neutral range state is established in which rotational power is not transmitted.
Typically, the tooth tip of the clutch sleeve and the tooth tips of the low and high gears have a bevel called a chamfer. The chamfer allows teeth to smoothly engage with each other.
As is known in the art, the chamfer includes a double chamfer (e.g., the tooth tip is beveled into a pointed shape, such as an isosceles triangle, as viewed from the top), and a single chamfer (e.g., the tooth tip is diagonally beveled into a shape, such as a right triangle, as viewed from the top). Note that, for example, if forward rotational power (forward torque) is mostly required, the single chamfer is employed to improve the ability of the clutch sleeve to engage with another component.
Incidentally, consider that the ranges are changed while the output shaft of the transmission mechanism is stopped, for example, when a vehicle is stopped. When the clutch sleeve is slid in order to change the ranges, the tooth tip of the clutch sleeve may abut the tooth tip of the low gear or the high gear, so that the clutch sleeve may not be further slid, and therefore, the current range may not be changed to the target range.
In Patent Literature 1, as described in paragraphs 0031-0037, when the clutch sleeve becomes unable to slide and gets stuck, the clutch sleeve is slid to return to a range position that was before trying to change the ranges for the purpose of preventing the clutch sleeve from being left in the stuck position for a long time.
In Patent Literature 2, as described in FIGS. 3 and 4 and paragraphs 0014-0019, for the purpose of preventing the sleeve from being stopped somewhere (a neutral position) between the high-speed side and the low-speed side during changing of the ranges, the sleeve is slid by high energy that is accumulated to a level sufficient to move the sleeve from the high-speed side to the low-speed side or from the low-speed side to the high-speed side.